Self-Referenced Optical Fiber Sensor with Stimulated Brillouin Scattering

Abstract

A sensor is used to measure a physical quantity and includes at least: a measurement optical fiber including at least one Bragg grating; optical means designed to inject, into the fiber, a first, “pump” wave at a first optical frequency and a second, “probe” wave at a second optical frequency, the second optical frequency being different from the first optical frequency, the Bragg grating being designed to reflect the first and second optical waves, and the optical power of the first wave being sufficient to give, after interaction with the second wave reflected by stimulated Brillouin scattering, a “Stokes” wave, the frequency of which is representative of the physical quantity to be measured; and means for analyzing the difference in frequency between the two, “pump” and “Stokes”, optical waves. The sensor may notably be used as a hydrophone.

1 . An optical fiber sensor for measuring a physical quantity comprising at least one measurement optical fiber having at least one Bragg grating, and further comprising:
 optical means designed to inject, into the fiber, a first, “pump” wave at a first optical frequency and a second, “probe” wave at a second optical frequency, the second optical frequency being different from the first optical frequency, the Bragg grating being designed to reflect the first and second optical waves, and the optical power of the first wave being sufficient to give, after interaction with the second wave reflected by stimulated Brillouin scattering, a “Stokes” wave, the frequency of which is representative of the physical quantity to be measured; and   means for analyzing the difference in frequency between the two, “pump” and “Stokes”, optical waves.   
     
     
         2 . The optical fiber sensor as claimed in  claim 1 , wherein the difference in frequency between the first wave and the second wave is of the order of 10 GHz. 
     
     
         3 . The optical fiber sensor as claimed in  claim 1 , wherein the optical fiber is a fiber made of a chalcogenide-based glass or an optical fiber made of bismuth-doped silica. 
     
     
         4 . The optical fiber sensor as claimed in  claim 1 , wherein the sensor is a strain sensor, the physical quantity to be measured being a mechanical strain applied on the fiber. 
     
     
         5 . The optical fiber sensor as claimed in  claim 4 , wherein the sensor is a hydrophone. 
     
     
         6 . An array of optical fiber sensors as claimed in  claim 1 , wherein all the sensors are arranged in series on one and the same optical fiber and in that the array includes a wavelength multiplexer placed between said fiber and the analysis means.